Course Information – 3.3 Species Diversity

Measures of Species Diversity

Species Accumulation Curves

Used to show when sampling is complete and all species have been identified
Quantifies the number of species found (y) per sampling effort (x).

N samples

Extrapolation Curves

Fit to data from an Accumulation curve to estimate how many species there might be.

N samples

Comparing Sampling Efforts

At which site would you expect to document more species?

Probably at Site 1, where sampling effort is greater.

How can we test whether site differences are meaningful?

We can rarefy our counts.

Rarefaction randomly selects a subset of observations from each site to equalize the sampling effort.
The resulting rarefaction curve can be used to compare species richness at the same level of sampling effort.

N samples

Species Diversity and Sampling Effort

Scales of Biodiversity

If funds were available to protect only one mountain range, which should be selected?

Region 2: the greatest gamma (total) diversity.

If funds were available to protect only one mountain, which should be selected?

Region 1: the greatest alpha (local) diversity.

If region 3 were selected for protection:

The relative priority of the individual mountains should then be judged based on the relative rarity of the assemblages.

Biodiversity indexes for three regions, each consisting of three separate mountains. Each letter represents a population of a species; some species are found on only one mountain, while other species are found on two or three mountains. Alpha, gamma, and beta diversity values are shown for each region. If funds were available to protect only one mountain range, region 2 should be selected because it has the greatest gamma (total) diversity. However, if only one mountain could be protected, a mountain in region 1 should be selected because these mountains have the highest alpha (local) diversity, that is, the greatest average number of species per mountain. Each mountain in region 3 has a more distinct assemblage of species than the mountains in the other two regions, as shown by the higher beta diversity. If region 3 were selected for protection, the relative priority of the individual mountains should then be judged based on the relative rarity of the assemblages.